Frequency division multiplexing and echo cancellation provide two schemes for full duplex MDSL implementation. Echo cancellation allows upstream and downstream signals sharing the same frequency band, therefore potentially offers higher data rate. However, it is well believed that the computational complexity prohibits the practical implementation of echo cancellation for discrete mulitone (DMT) signal transmission.
FIG. 1 shows a traditional echo cancellation system. At the DMT receiver, the incoming data y.sub.n mixes with the echoed transmission data s.sub.n. This mixed data stream passes a common time domain equalizer (TEQ), and subtracts a synthesized echo stream after the TEQ. Since synthesizing an echo signal generally requires time domain convolution with a large number of taps, it is computationally expensive.